Air cooling system with recirculating passageway



Dec. 11, 1956 c. COBLENTZ 397735356 AIR COOLING SYSTEM WITH RECIRCULATING PASSAGEWAY Filed May 25, 1954 2 Sheets-Sheet 1 IN V EN TOR.

Dec. 11, 1956 c, COBLENTZ 2,773,356

AIR COOLING SYSTEM WITH RECIRCULATING PASSAGEWAY Filed May 25, 1954 2 Sheets-Sheet 2 m m m be 3 8c l. mu. 4i??? FIG. 4 v

f INVENTOR. W 6 517%? W fi m United States Patent AIR COOLING SYSTEM WITH RECIRCULATING PASSAGEWAY Robert C. Coblentz, Erie, Pa.

Application May 25, 1954, Serial No. 432,274

6 Claims. (Cl. 62-6) In air conditioning systems controlled solely by room temperature, the primary load on the system is the removalof sensible heat. This invention is intended to achieve the same or better comfort level by recirculation of part of the cooled air over the evaporator or cooling coil so the capacity of the unit is more efficiently used for removal of moisture and consequently a smaller unit will achieve the same comfort level without as great a reduction in temperature. Use is made of a device responsive to the temperature of the cooled air for cutting down the recirculation at temperatures which would cause frosting of the cooling coil. This allows more effective dehumidification without the need for complicated humidity controls. Because of the lower temperature of the cooled air, the unit is protected from excessively low temperatures. Bringing in outside air for ventilation when the cooled air reaches the desired low temperature is an additional expedient protecting the cooling coil from frosting and at the same time providing air needed for ventilation.

In the accompanying drawings, Fig. l is a diagrammatic view of an air cooling system; Fig. 2 is an enlarged detail of the damper and associated control mechanism used in Fig. 1; Fig. 3 is a fragmentary view showing the damper control used in an air conditioning unit where the fan is arranged on the upstream side of the cooling coil and blows the air through the cooling coil; Fig. 4 is a fragmentary view of another arrangement of the damper which recirculates part of the air delivered by the fan back to the fan inlet without going through the cooling coil; Fig. 5 is a fragmentary view of another modification in which an auxiliary fan is used to recirculate cooled air back over the cooling coil; Fig. 6 is a fragmentary view of another modification in which a humidistat determines whether the recirculated air passes back over the cooling coil, or merely to the suction inlet of the fan; Fig. 7 is a detail of another arrangement for adjusting the damper control; and Fig. 8 is a diagrammatic view of a window air conditioning unit.

In the air cooling system shown in Fig. 1, the conventional parts are readily identified, 1 being the cabinet having in its lower part an intake grill 2 and in its upper part an outlet grill 3 for discharge of the cooled air. In the lower part of the cabinet is mounted a refrigerating system having a compression 4 driven by a motor 5, a condenser 6, and sub-freezing cooling coil 7 arranged between the inlet and outlet grills 2 and 3. Above the cooling coil 7 is a blower or fan 8 having an inlet 9 and an outlet 10 discharging through a partition 11 which forms in conjunction with the top of the cabinet 1 a chamber leading to the outlet grill 3. The fan 8 runs all of the time. The motor 5 runs to provide refrigeration whenever a room thermostat 12 calls for cooling. A duct 13 leading through an outside wall 14 to a fresh air intake grill 15 provides for the supply of fresh air needed for ventilation. The parts so far described are or may be of common construction and may ditfer substantially in appearance from the diagrammatic illustration.

Between the upper part of the cooling coil 7 and a part of the casing 16 for the fan 8 in which there is developed a substantial air pressure is arranged a recirculating duct 17 having at the fan casing end a damper 18 which directs some of the air within the fan casing 16 back through the duct 17 and through the cooling coil 7 so as to recirculate this air through the cooling coil. This recirculation substantially lowers the temperature of the air and accordingly removes additional moisture. I

Because of this recirculation, the volume of air flowing through the fan outlet 10 to the outlet grill 3 is decreased, but the air which does flow through the outlet grill is of lower temperature and accordingly contains less moisture. The net result of the recirculation is a lowering of the humidity in the room without as great a drop in the room temperature thereby achieving the same or better comfort level than as though the recirculation were omitted.

Because of the recirculation, the air flowing through the cooling coil is of lower temperature and there is a tendency for the cooling coil to frost, sometimes even to the extent of completely blocking the passages through a the cooling coil. It is necessary that the temperature of the cooled air leaving the coil 7 be kept above the excessive low temperatures at which the coil frosts. This is accomplished by a thermostatic bellows 19 mounted within the recirculating duct 17 and accordingly responsive to the temperature of the cooled air and connected to a lever 20 pivoted at 21. The lever 20 and the damper 18 are rigidly connected together so that they in effect comprise a bell crank lever. The thermostatic bellows 19 is commonly liquid filled with a liquid which at some low temperature, for example, -45 F., contracts sufficiently to move the damper to a position closing the upper end of the recirculating duct 17. When the damper 18 closes the recirculating duct, the air coming into the unit through the intake grill 2 makes only one pass through the cooling coil 7 and is discharged directly by the fan to the outlet grill 3. With only one pass through the cooling coil, the air discharged to the room through the grill 3 will be above the temperature at which the cooling coil frosts. If the air discharged to the room through the outlet grill 3 drops to a frosting temperature for the cooling coil 7 with the recirculation shut off, the room temperature will be so low that the room thermostat 12 will shut down the refrigeration unit and stop the cooling.

Under normal conditions, the temperature of the cooled air discharged to the room through the outlet grill 3 will be above the dangerously low temperatures at which frosting of the cooling coil 7 occurs and the damper 18 will accordingly deflect a substantial proportion of the output of the fan 8 back through the recirculating duct 17 and through the cooling coil 7 to the intake side. This recirculated air flowing through the recirculating duct 17 makes two additional passes through the cooling coil 7, and accordingly has its temperature very closely approaching that of the cooling coil. The moisture content is accordingly greatly reduced, which lowers the relative humidity in the room and achieves the same comfort level at higher room temperatures. The amount of air which should be recirculated through the duct 17 will naturally be greater under high humidity atmospheric conditions than under low humidity conditions. For high humidity conditions in a unit delivering 1,000 cubic feet of air per minute to the room, as much as 1,500 cubic feet of air per minute may be recirculated through the duct 17 and under such conditions, the temperature of the cooled air discharged to the room may be in the range of -50 F. as compared to F. for the same unit without recirculation. Furthermore, the cooled air discharged to the room will have a lower relative humidity because it is a mixture of air which has had on the average one pass through the cooling coil 7 with additional air recirculated through the duct 17 and having two additional passes through the cooling coil 7.

The control of the damper 18 by the thermostatic bellows 19 is entirely independent of the room thermostat 12. Such bellows ordinarily have a stop limiting the expansion so that no matter how high the temperature becomes, the damper 18 can never move beyond the position determined by this stop. This sets the maximum amount of recirculated air. As the temperature of the cooled air delivered to the room falls, the liquid within the thermostaticbellows 19 contracts and as it approaches the low limit at which frosting of the cooling coil '7 becomes imminent, the bellows 19 contracts and moves the damper 18 toward the closed position. The damper 18 reaches the fully closed limit at the low limit and thereafter all the cooled air flowing through the cooling coil 7 is discharged directly to the room through the outlet grill 3 without any recirculation.

Fig. 2 is a detail of the bellows including an adjustment for the maximum open position of the damper 18 diagrammatically illustr ated at 22 in Fig. l. The thermostatic bellows 19 is fixed at one end to a bracket 24 on a frame 25. At the other end of the thermostatic bellows 19 is a stem 26 which projects out through a clearance opening 27 in a bracket 28 likewise fixed to the frame 25. The stem 26 is pivoted at 29 to a bell crank lever 30 pivoted at 31 to the frame 25. One arm 32 of the bell crank lever is fixed to the outer casing 33 of a flexible shaft having a shaft 34 longitudinally slidable therein. The casing 33 is of sufficient length so that it will accommodate the maximum pivoting of the bell crank lever 30 Without appreciable restraint. The position of the shaft 34 within the casing 33 is adjusted by the knob 22 fixed to the shaft 34. By pushing and pulling on the knob 22, the shaft 34 is slid in and out of the casing 33 and its free end 35a attached to a damper 18a pivoted at 21a on the arm 35 of the bell crank lever 30 adjusts the full open position of the damper 18a controlling the amount of air recirculated. The thermostatic bellows is shown in its maximum expanded position limited by the bracket 28 and the damper 18a is accordingly in its full open position. As the temperature drops, the bellows is contracts and pivots the bell crank lever 30 about the pivot 31 moving the damper 18a toward the closed position. As the damper 18a is moved away from the arm 35, by pulling outward on the knob 22, the damper is moved toward the closed position cutting down the amount of air recirculated so that under conditions where the humidity is not objectionably high, the amount of airrecirculated over the cooling coil can cut down.

In addition to the damper 13, which shuts off the recirculation when the temperature of the cooled air delivered to the room reaches a low enough value so that frosting of the cooling coil is imminent, there is also in the Fig. l cooling system another thermostatically controlled damper 36 controlled by a thermostatic bellows 37 which opens-and brings in outside air through the duct 13. So long as the temperature of the cooled air delivered to-the room through the outlet grill 3 is above the frosting value, the bellows 37 keeps the damper 36 closed. As soon as the temperature of the cooled air approaches thedangerously low value, the thermostatic bellows 3'7 contracts and moves the damper 36 to an open position at which air is drawn in through the duct 13. The thermostaticbellows 37 is positioned with relation to the cooling coil 1S0 that .it is effectively responsive to the temperatureof the cooled air delivered through the outlet grill 3. The amount of outside airdrawn-into the duct 13 under these conditionsis controlled by an auxiliary manually'adjustabledamper '33. Since under conditions when air cooling is necessary, :the outside air'temperature will be higher than the room air temperature, the thermostatically controlled damper 36 provides an additional expedient for preventing frosting of the cooling coil 7.

Because the cooling air temperature is lower in the Fig. 1 air cooling system when there is recirculation through the duct 17, it is desirable to protect the refrigerating unit from excessively low evaporator temperatures. This is accomplished by a thermostat 39a on the suction line 40 leading from the cooling coil evaporator 7 back to the intake of the compressor 4. This thermostat 39a is in series with the room thermostat and controls a switch 39b to shut down the refrigerating unit whenever the temperature of the refrigerant in the cooling coil evaporator 7 reaches a dangerously low value.

In some air cooling systems, the fan is arranged below the cooling coil so as to blow air through the cooling coil. in such air cooling systems, as diagrammatically illustrated in Fig. 3, the fan has a discharge outlet 8b leading directly to theunderside of the cooling coil 7 and the.

entire space above the cooling coil constitutes a plenum chamber leading to the outlet. in such air cooling systems, the benefits of recirculation for dehumidification are obtained by a thermostatically controlled damper 18]) positioned by a thermostatic bellows 1%. So long as the temperature of the cooled air discharged to the room is above the temperature at which frosting of the cooling coil takes place, the damper 18b occupies the position illustrated in Fig. 3 and deflects a substantial portion of air back through the section 7b of the cooling coil. When the temperature of the cooled air reaches a danger ously low value, the thermostatic bellows 19b contracts moving the damper 18b to the closedposition indicated in dotted lines and shutting off the recirculation. The thermostatically controlled damper 18b is entirely within the unit and as in the Fig. 1 system is independent of the room thermostat or other controls.

Instead of recirculating air back through the cooling coil, somewhat less efiicient results can be obtained by the construction shown in Fig. 4 where a thermostatically controlled damper 18c controlled by a thermostatic bellows 190 is arranged in the discharge outlet of the fan 8c so as to deflect a portion of the air normally dischargedto the outlet grill back to the fan inlet 90. This cuts down the volume of air discharged to the room and accordingly cuts down the velocity of air flow over the cooling coil and results in a lower temperature of the cooled air. As in the previously described constructions, when the temperature of the cooled air reaches the frosting value, the thermostatic bellows 19c contracts and closes the damper 180.

By supplementing the Fig. 4 system with an auxiliary fan 37 havingits motor 38 controlled by a humidistat 39, the air recirculated underthe control of the damper can be forced back through the cooling coil 70 so as to further cool the recirculated airand thereby lower the humidity. With this combination, further cooling of the air for dehumidification is obtained under the control of the room humidistat 39.

The cooling system of Fig. 6 adds to the Fig. 4 system a duct 40 leading from the damper 180 back to the cooling coil 70. This duct '40 has an additional damper 41 controlled by a solenoid 42 in circuit with a room humidistat 43. Whenever the room humidistat calls for dehumidification, the solenoid 42 is energized closing the damper 41 in which case the cooled air has the same recirculation as in the Fig. 1 system. Because the thermostatic bellows is set to close the damper 180 when the cooled air reaches the frosting temperature, the cooling coil 7c is protected from frosting, as in the Fig. 1 system. Whenever the room humidity is satisfactory, the solenoid 42 is de-energized and the damper 41 opens thereby permitting the air recirculated past the'damper 180 to How directly to the fan inlet 90.

Fig. 7 shows an arrangement alternative to "Fig. 2 for adjusting the full open position of the damper 18d-controlling the recirculation. In this arrangement, the thermostatic bellows 19d is carried on a frame 44 slidably mounted on a frame 45 carrying an adjusting screw 46 threaded into a nut 47 fixed to the frame 44. By turning the adjusting screw 46, the frame 44 with the bellows carried thereby is moved toward and away from an opening 48 through which the recirculated air must pass. This controls the amount of air recirculated when the damper 18d is in its fully open position by hinging the damper about pivot 21d on the frame 45.

Fig. 8 shows part of a window air conditioner having a cabinet 49a with an air intake grill 49 and a cooled air outlet grill 50. The air flowing through the intake 49 passes over a cooling coil 51 into the inlet 52 of a fan 53 driven by a motor 54. Between the outlet 55 of the fan and the cooling coil is a recirculating duct 56 controlled by a damper 57 positioned by a thermostatic bellows 58 in the duct leading to the outlet grill 50. By suitable adjustment, the damper can be set to recirculate the desired portion of the cooled air back over the cooling coil for dehumidification. At excessively low temperatures, the damper closes the duct 56 to prevent frosting of the cooling coil.

In all forms, the recirculating duct can be withinthe cabinet of the air conditioning unit so there are no problems of providing air tight connections. Nor is it necessary to insulate the recirculating duct to prevent condensation. The control by the temperature of the cooled air is adaptable to modification of existing installations in which the benefits of additional dehumidification are desired.

What is claimed as new is:

1. In an air cooling system, a casing having an intake for air to be cooled and an outlet for cooled air, a sub freezing cooling heat exchanger within the casing in the path of the air flow between and spaced from the intake and outlet, a fan within the casing for producing a forced circulation of air from the intake over the heat exchanger to the outlet, the flow of air from the inlet side to the outlet side of the heat exchanger being unrestricted, a recirculating passageway within the casing spaced from and between the intake and the outlet from the casing and leading from the outlet side of the heat exchanger back to the intake side of the heat exchanger, a damper within the casing associated with the recirculating passageway and arranged on the outlet side of the heat exchanger at a point at which the cooled air has a positive pressure for deflecting part of the cooled air back from the outlet side of the heat exchanger through said passageway to the intake side of the heat exchanger for further cooling, and a thermostatic device within the casing and responsive to the temperature of the cooled air in the casing for moving the damper to cut down the flow of air through the recirculating passageway at a preselected low temperature of the cooled air in the casing.

2. In an air cooling system, a casing having an intake for air to be cooled and an outlet for cooled air, a subfreezing cooling heat exchanger within the casing in the path of the air flow between the intake and outlet, a fan having a housing within the casing and having a suction inlet on the outlet side of the heat exchanger for producing a forced circulation of air from the intake over the heat exchanger to the outlet, a recirculating passageway within and spaced from the casing and branching from the fan housing and leading back to the intake side of the heat exchanger, a damper in the fan housing associated with the recirculating passageway and arranged at a point at which the cooled air has a positive pressure for deflecting part of the cooled air back through said passageway to the intake side of the heat exchanger, and a thermostatic device within the casing and responsive to the temperature of the cooled air in the casing for controlling the damper to cut down the flow of recirculated air at a preselected low temperature of the cooled all,

3. In an air cooling system, a casing having an intake for air to be cooled and an outlet for cooled air, a subfreezing cooling heat exchanger within the casing in the path of the air flow between the intake and outlet, a fan having a housing within the casing with a suction inlet on the outlet side of the heat exchanger for producing a forced circulation of air from the intake over the heat exchanger to the outlet, 2. recirculating passageway within and spaced from the casing branching from the fan housing on the pressure side and leading to the suction side of the fan, and a damper within the casing associated with the recirculating passageway and arranged at a point at which the cooled air has a positive pressure for deflecting part of the cooled air back through said passageway.

4. in an air cooling system, a casing having an in take for air to be cooled and an outlet for cooled air, a sub-freezing cooling heat exchanger within the casing in the path of the air flow between and spaced from the intake and outlet, a fan for producing a forced circulation of air from the intake over the heat exchanger to the outlet, the flow of air from the inlet side to the outlet side of the heat exchanger being unrestricted, a recirculating passageway leading from the outlet side of the heat exchanger back to the intake side of the heat exchanger, said passageway being subject to a positive pressure forcing part of the cooled air back through said passageway to the intake side of the heat exchanger, and a control for the air flow through the recirculating passageway responsive to the temperature of the cooled air in the casing for cutting down the flow of air through the recirculating passageway at a preselected low temperature of the cooled air.

5. In an air cooling system, a casing having a room air intake, a fresh air intake and an outlet for cooled air, a cooling heat exchanger within the casing in the path of the air flow between the intakes and outlet, a fan within the casing for producing a forced circulation of air from the intakes over the heat exchanger to the outlet, at recirculating passageway within the casing leading from the outlet side of the heat exchanger back to the intake side of the heat exchanger, said recirculating passageway being subject to positive pressure forcing part of the cooled air from the outlet side of the heat exchanger back through said passageway to the intake side of the heat exchanger, a damper control for the fresh air intake, and a thermostatic device responsive to the temperature of the cooled air for moving the damper to increase the incoming flow of fresh air at a preselected low temperature of the cooled air in the casing.

6. In an air conditioning system, a cabinet having therein a cooling coil, a centrifugal fan having its axis of rotation transverse to the cooling coil and the fan housing spaced axially from the cooling coil with its inlet presented to the cooling coil and its outlet directed parallel to the cooling coil, a discharge duct leading from the fan outlet to the outside of the cabinet, a recirculating duct within the cabinet bridging the space between the fan outlet and the cooling coil, a damper extending into the fan outlet for directing cooled air back through the cooling coil, and a thermostatic means mounted in the discharge duct for controlling the damper.

References Cited in the file of this patent 

